How to reduce hum with phono preamp

[stereoaddict]

I too had the same problem with low (bass) frequency hum with my current pre-amp ($20 Behringer pre-amp), I have my turntable hooked to the pre-amp connected to a BSR equalizer connected to my receiver and I believe I have eliminated the hum now by simply relocating the pre-amp, I believe there was some sort of interference. I used masking tape to secure the pre-amp to the back of my TV stand which is behind my receiver and to the left of the turntable and it seems to be working beautifully... give this a shot before trying all this other crazy stuff.

 

[mahiruha]

The reason hum varies with the position of the pre amp beacuse the cable from the turntable that goes into the pre amp acts as an antenna so as you move the pre amp it moves the cables so the amplitude of the signal it catches varies. Moving your pre amp is a solution I agree but it is not a very rigid solution the best thing is to replace the cable from turn table to phono pre with a very good shielded cable since that cable carries the most faintest of signals and most prone to catch outside interference.

 

[bottle]

how much were the audioart cables ? I was facing hum with the stock ic's but it reduced with some other old ic i had

 

[mahiruha]

Ask Sridhar from ARN Systems for audio art pricing.

 

[Heemee]

I register this forum to say thank you!! Finally my hum/ hiss issue begone!! I opened up my vintage Luxman direct drive, changed the interconnects to a set of good quality shielded cables. I am using Belden 1505f (versatile video cable - perfect for tonearm to phonostage interconnects; low capacitance 17PF/feet) And Wala! Not only is the hum issue solved, even the sound improved a tad! Once again thank you for providing the solutions. Cheers

 

[jagdish_p]

I was thinking in this line the problem is the interconnect and ground wire is hardwired in the TT body for Project Debut III. Is there anyway I can offer more shielding to the existing cable. Some sort of Teflon pipe. Not sure if such a thing exists.

Thanks.

Yes, you should be able to buy a Teflon pipe or even Teflon tape that you can wrap over the wire completely. Concentrate on doing this for the signal IC ignore the ground wire for now
cheers

Vasu is right, Teflon tape is also called plumbers tape. The material is very distinct and should be easy to make out. Teflon tubling should be available in any electronics parts/cables store

Cheers

Teflon does not offer any electrical shielding , it is only a mechanical shield against physical damage and hence can not reduce electrical noise.

On the other hand a metallic conductor like an Aluminum foil can act as a shield against electrical hiss/hum pick up.

 

[jmascreen]

Reviving a old thread.. I am facing the same issue as mentioned above by when i disconnect the TT cables still I have the hum and I feel the Phono Pre is the culprit. Any idea on how to fix this. I have the CNC phono.

 

[omishra]

Connect TT ground to phono pre ground lug at backside. Or required same time to Power Amp ground lug or chassis.

 

[reubensm]

Reviving a old thread.. I am facing the same issue as mentioned above by when i disconnect the TT cables still I have the hum and I feel the Phono Pre is the culprit. Any idea on how to fix this. I have the CNC phono.

Are you running on batteries or on a step-down psu?

 

[aks07]

Does the hum increases/decrease when you rotate the volume pot?

Disconnect the TT cable and short to ground the phono stage input. Crank up the volume. If the hum is gone than it is a shielding issue between the cartridge and phono stage.

If the hum is still present then either it is being generated by the phono stage ( check construction specially grounding, power supply etc) or it is a ground loop issue.

In a properly setup phono system hum will be zero but minute background noise could be present.

 

[jmascreen]

Are you running on batteries or on a step-down psu?

Not on batteries. a PSU

 

[jmascreen]

Connect TT ground to phono pre ground lug at backside. Or required same time to Power Amp ground lug or chassis.

Its already connected to Phone Pre ground lug at back. If I disconnect the TT completely from Phono still i get the hum.

 

[jmascreen]

Does the hum increases/decrease when you rotate the volume pot?.

Yes it increases/decrease but its starts audible around 8 PM of volume pot

Let me try the following today.

Disconnect the TT cable and short to ground the phono stage input. Crank up the volume. If the hum is gone than it is a shielding issue between the cartridge and phono stage.

If the hum is still present then either it is being generated by the phono stage ( check construction specially grounding, power supply etc) or it is a ground loop issue.

In a properly setup phono system hum will be zero but minute background noise could be present.

 

[sachu888]

There could be a problem with your TT's interconnect.

Regards
Sachin

 

[Selvin]

Reviving a old thread.. I am facing the same issue as mentioned above by when i disconnect the TT cables still I have the hum and I feel the Phono Pre is the culprit. Any idea on how to fix this. I have the CNC phono.

I understood as below.

You are connected your TT to CNC Phono stage. CNC Phono Stage output to one of Amp line Input. TT Ground wire is connected with CNC Phone Ground. Hum is listenable even at listening position. If yes try the following.

1. Disconnect all wires related to TT and Phono Stage and check. Still hum is there problem is with Amp else continue further.
2. Keep TT is completely disconnected. Short input terminals of phonostage. Connect the interconnect between Amp and Phonostage output and power up Phonostage. If hum is there it is originated to either inter connect or Phonostage and try the following.
a) Check with other Interconnects.
b) Try with only Left then only Right channel and try to narrow the culprit.
c) Check your power supply '0' point solidly grounded on Phonostage cabinet.
d. Check is there any ground loop in the circuit wiring.
e. If your phonostage is assembled on some non-metallic cabinet try to shield the PCB and shield should be grounded.

3. If you not here hum at stage 2 the problem is associated with TT. Try below.
a) Check the continuity between Phonostage Ground point to power supply '0' point.
b) Check the continuity between TT tonearm metal part to Phonostage GND point once the TT is connected. If continuity is not ok the tonearm GND wire wiring need to be check.
c) Check also the Phono cable of TT for continuity and any dry soldering etc.

In few older TT the GND wire, Left, Right channel interconnect shields and Cartrige -ive are connected inside the TT at a single point. In such case little hum close to speaker is normal. Such cases if the GND wire of the TT disconnected from the Phonostage GND and hum vanish most of the time.

Wishes to fix the issue.

 

[reubensm]

if I were you, I would first replace the PSU with batteries and check if the hum still exists. If it does not, then I'd check the PSU filtering. If it does not, then I would proceed with the rest of the checks.

 

[omishra]

Saw pics of his CNC phono. His PS hanging vertical near output pads and an EI transformer with couple of mm away from CNC phono within same box. Also all seems to be in plastic box.
I Suggested him to move transformer in to separate wallwart adapter case.

 

[reubensm]

Saw pics of his CNC phono. His PS hanging vertical near output pads and an EI transformer with couple of mm away from CNC phono within same box. Also all seems to be in plastic box.
I Suggested him to move transformer in to separate wallwart adapter case.

that's the reason for sure.

 

[pappu]

Mr. Mahiruha,

So far as your is concerned there may be two things happenning for that hum. Either the speaker is too close to Turn Table so you are getting a feedback sound or The wire from turntable to Pre- Amp is not well shielded. You need to use a good quality shield wire for connecting those TT and Pre Amp and try to make it as short as possible. I want to know another thing are you using only TT or a record player which have amplifier inside. But you r not using that.


Thanks.

 

[pappu]

ALso look at the earthing connection of the TT . Check that TT's earting is connected to chessis of TT or not If yes then is Chessis the also the Ground. If yes the. Good shield wire will do the job. If you see that the earthing connection is connected to some other parts of TT and it is not ground . Then You needd to Ground it .